This invention relates generally to a wristwatch of the type having means to display auxiliary functions other than timekeeping functions and more particularly to a wristwatch providing an indication when battery voltage has fallen below a prescribed level. It is an important function of an electronic watch to alert users to an approaching termination of the battery life, which presents the danger that the watch will stop operation. A warning is required before the battery has insufficient capacity remaining to operate the watch. In one example of a battery-life indication device, there exists means to warn of the danger of low voltage by detecting the voltage of the battery as the battery life approaches its termination. When the voltage is low, an abnormal display is provided as compared to the display normally presented on the face of the wristwatch. The abnormal display includes, for example, advancing the second hand by an amount corresponding to two seconds at each movement and then stopping the movement of the hand for two seconds.
However, power consumption of electronic watches has been remarkably decreased so that watches can be produced having long battery life, for example, five years. Among such watches, there are watches which have an even longer battery life, in the order of seven to eight years, depending upon variations among batteries and the temperatures in which the watch is worn. As a result, though a battery-life indication device is specially provided in a wristwatch, the user may forget the abnormal characteristics of the battery-life indication mode of operation because a considerably long time has elapsed since the user has purchased the watch. The user is fearful that something is wrong with the watch when, because of low battery voltage, the second hand suddenly starts to advance by increments corresponding to two seconds.
Also, it is wasteful to incorporate single-function special circuits, e.g., a low-voltage battery-indicating circuit, because it is so infrequently put to use in the conventional prior art timepieces. Provision of auxiliary functions often raises the cost of manufacture and increases the complexity of the design. The additional functions may be, for examples, a chronograph or a facility for correction of differences in time. These functions supplement the conventional timekeeping and display functions.
In a conventional prior art watch having an analog time display with hands for hours, minutes and seconds, when an additional function is added, the visual motion of the indicating portion displaying such hours, minutes and seconds is made to perform differently from the normal movement, so that the different movement of the indicating portion serves as an identification of the additional function. For example, Japanese Patent Publication No. 49-71968, laid open under No. 13280/76, discloses that an approaching termination of battery life is indicated by having the second hand move two quick steps once every two seconds when battery voltage drops. Normally, the second hand moves uniformly every second. Further, a different state from the normal state of a watch is shown by using a light-emitting diode on the face of the wristwatch, which, for example, may indicate low battery voltage. Still further, there is a watch design in which the hand movement serves an additional function, for instance, the second hand is used both as the second hand per se and as a hand for setting the alarm time. There is also an embodiment wherein the movement of a hand serves a special function and an additional function is displayed by using another member such as a light-emitting diode.
However, a function, for example, for displaying a diminution in battery-life expectancy is operated and displayed only during the one to two weeks of a battery life extending for two to five years of normal wearing time, i.e., when the battery voltage is getting low. The electric load caused by having a special electronic circuit and a separate mechanical function for detecting this drop of battery voltage becomes large. Thus, incorporation of the function does not always justify the cost in financial terms or in battery life or design complexity.
What is needed is an electronic watch which provides for independent actuation or previewing of infrequently used functional modes of operation, and combines a plurality of functions in a few circuits and with but a minimum of external members.